Theo, Chris, Steve,
I am also a big fan of Carroll Smith's books and trust in his wisdom and
experience. This subject is particularly timely for me because I've been
bothered for about a year now by what I thought was a "warped rotor" -
specifically, the rear rotors on my Lincoln LS. The problem started shortly
after I installed new brake pads. I did nothing in particular to bed them
in, and that was probably my undoing. To exacerbate the problem, I park on
an incline in my driveway and, consequently, tend to apply the parking brake
firmly when I park at home. I kept thinking a) it will get better (after ~1
year it hasn't) or b) I'll get the rotors turned or better yet get some
better quality (i.e., won't warp) aftermarket rotors. After reading Smith's
article and your comments, I decided maybe my rotors didn't need turning (or
better yet, Blanchard grinding) and would try fixing them myself. I pulled
the calipers and used a power drill and a coarse abrasive disk that's made
of something like the material that Scotch Wool is made of to resurface the
disks. I worked primarily along the diametral direction until only new fresh
surface showed. The surface ended up being somewhat cross/hatched. I then
installed a new set of pads and proceeded to bed them in per Smith's
instructions. Another advantage of the cross-hatching is you can easily see
the progress of the bedding in. Now, the vibration I previously had when
braking is completely gone and the brakes also work much better than before.
I've usually done a bedding in with the Tiger, but now I'm a believer in
bedding in pads on any vehicle. As for the question of warping, the problem
that occurs with hot brakes and then setting the parking brake becomes one
of cementite formation on the disk surface instead of warping. But what
about warping from not evenly tightening the lug bolts? Fact or fiction?
BTW, more than you'll probably ever want to know about cementite and why
gray iron is the perfect material for disk brakes can be found at:
www.sae.org/events/bce/tutorial-ihm.pdf
My thanks to Theo, Steve, and Chris for bringing this very helpful
information to our attention. There's no List like the Tiger List!!
Best regards,
Bob
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